1. Field of the Invention
The present invention relates to the manufacture of books and particularly to the assembly of book blocks by sewing individual block sections together. More specifically, this invention is directed to apparatus for sewing together book block sections and especially to sewing apparatus which sequentially performs pre-piercing and sewing operations while preventing undesired relative movement between the block section and a sewing saddle on which it is supported. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
In a known method for thread-sewing book block sections together to define a book block, a sewing needle punches a thread through the fold of each individual block section, and this thread is transferred to a hook needle which is then thrust through the fold at a distance from the sewing needle. The hook needle carries the thread, in the form of a loop, out of the block section and causes it to be linked with a previously formed loop associated with the preceding block section. The apparatus for performing the above-briefly described sewing technique is known in the art as a "sewing-press". A conventional sewing press consists of a sewing head, an oscillating sewing saddle and a delivery table for discharging the sewn book blocks. The sewing saddle feeds the individual book blocks sections to the sewing head where the above-described sewing method is performed. A sewing saddle customarily includes a pre-piercing mechanism. The pre-piercing mechanism is equipped with a linear array of needles which perforate the book block section, typically from the inside to the outside, at predetermined locations along the fold "gutter". The object of the pre-piercing is to minimize the resistance which will be encountered by the sewing and hook needles, which are subsequently punched through the fold gutter, thereby minimizing needle misalignment and breakage.
The initiation of operation of the pre-piercing mechanisms of prior art book block sewing apparatus occurs prior to the sewing saddle stopping in the sewing position. The pre-piercing needles, after punching through the block section fold gutter, are caused to return downwardly to their initial position and the block section is then moved into the position where the sewing needles and hook needles are forced through the holes which have been pre-pierced. Before entering the sewing position, the book block section will be engaged by a hold-down element, typically in the form of a leaf spring, which presses the block section against the sewing saddle during the pre-piercing operation.
The problem of possible book block section misalignment is of long standing in the art. Misalignment can occur as a result of the frictional forces between the book block spine and the hold-down element during the movement of the block section from the point at which the pre-piercing occurs to the sewing position. This misalignment is known in the art as "block section rolling" and results in the sewing needles missing the middle of the block section gutter which can cause the needles to break and the threads to snap. Furthermore, even if needle or thread breakage does not occur, a book block section containing block sections which have been sewn at locations offset from the fold is invariably of inferior quality and may result in breakdowns or production disruptions in the course of subsequent processing operations.